CHAP 13 : FOOD MICROBIOLOGY Flashcards
What are microorganisms?
Microorganisms are small organisms that cannot be seen with the naked eye.
What are the 2 main classes of miccroorganisms? Give examples.
- Prokaryotes : e.g. bacteria and archaea
2.Eukaryotes : Fungi, protozoa, animals
What are some characterisitics of prokaryotes?
- cells lack a membrane-bound nucleus and other membrane-bound organelles
- DNA present as 1 circular strand, complexed with proteins into a nucleoid
How is DNA organised in eukaryotes?
DNA is made out of multiple linear strabds, and each strand is organised into a chromosome
MICROORGANISM : BACTERIA
What is the structure of gram positive and gram negative bacteria?
- Gram positive : a thick peptidoglycan layer (up to 30 layers) on top, followed by plasma membrane below
- Gram negative : a thin layer of peptidoglycan in between outer surface membrane and plasma membrane of cell wall
MICROORGANISM : BACTERIA
What is peptidoglycan? Where is it found?
- Peptidoglycan is a polymer made of sugars and amino acids that forms a mesh-like layer outside plasma membrane of bacteria.
It is a component of the cell wall
MICROORGANISM : BACTERIA
What are the 3 functions of peptidoglycan?
- It protects bacteria from lysis due to turgor
- It protects bacteria cell from extreme environmental conditions
- It maintains the shape of the bacteria
MICROORGANISM : BACTERIA
What are the different shapes of bacteria and what are they called? [4]
- Cocci : round-shaped bacteria
- Bacilli : rod-shaped bacteria
- Spirilla : spiral-shaped bacteria
- Pleomorphic : bacteria that can have multiple forms or shapes
MICROORGANISM : BACTERIA
What are the 2 harmful substances tha bacterias can form?
- Spores and endospores
- Biofilms
MICROORGANISM : BACTERIA
What are biofilms and how do they form?
How can they pose a risk to food safety?
- Biofilms : clusters of bacteria that are attached to a surface and/or to each other and embedded in a self-produced matrix. Contains organic matter such as proteins, carbohydrates etc
- Free-floating microorganisms attach to moist ssurface using pili –> bacteria secrete various biomolecules –> a layer of slime forms around exposed surfaces of microorganisms
- Biofilms can form on food contact surfaces such as pipes (also resistant to cleaning sanitisers)
MICROORGANISM : BACTERIA
How do spores/endospores threaten food safety?
They are resistant to desiccation (removal of moisture) and heaat and may survive food processing conditions, may still be present in food after processing
MICROORGANISMS : Yeast, mould
What are 2 properties of yeast and mould?
- Considered as spoilage organisms
- Can grow at temperature, pH and water conditions that are not favourable for bacteria
MICCROGANISMS : Mould
How do mould feed into food or surfaces?
They form long filaments called hyphae, which further group to form mycelium. The filaments are used as roots to feed into the food / surfaces
(Analogy : its like putting your face into the food and letting your skin absorb the food)
MICROORGANSIMS : MOULD
Some moulds are potent because they produce ___ that can cause cancer
mycotoxins
MICROORGANISMS : PROTOZOA
What is protozoa and what structure do they have?
- Protozoa are single-celled organisms that do not have cell walls.
- They consist of nucleus and membrane bound organelles
MICROORGANISMS : PROTOZOA
Protozoa are all parasitic. True or false?
False, there are also some non-parasitic protozoa`
MICROORGANISMS : PROTOZOA
What are the characterisitics of parasitic protozoa? [2]
- They have been adapted to invade and live in cells and tissues of other organisms
- They derive nutrition directly from host. Although they dont directly kill hosts, they can cause severe harm
MICROORGANISMS : PROTOZOA
Where is Toxoplasma Gondii usually foundd and how is it transmiited?
- Commonly found in soil, faeces (esp cat faeces) and raw meat
- Commonly transmitted from cats to humans
MICROORGANISMS : PROTOZOA
What are the names of the 2 protozoa that are commonly associated with faeces-contaminated water?
- Cryptosporidium spp
- Giardia spp
*spp : species plurimae (species in the plural form)
MICROORGANISMS : PROTOZOA
What are the 2 functions of non-parasitic protozoa?
- Breaking down waste food
- Eat excess bacteria during water treatment
MICROORGANISMS : VIRUS
What is the structure of a virus?
A virus consists of single or double strands of RNA or DNA surrounded by a protein coat.
MICROORGANISMS : VIRUS
Viruses lack necessary machinery for replication and are not capable of metabolic activity by themselves. How then do they spread?
- They invade cells
- some viruses entirely go into the host cell
- bacteriophages inject their DNA/RNA into the cell - Use machinery and materials in cells
- release their genetic material and give instructions to cell to make more copies of the virus - and thus producing more viral molecules
MICROORGANISMS : VIRUS
How is Hepatitis A transmitted and what are its effects?
- Transmitted via oral-faecal route
- Causes liver inflammation
MICROORGANISMS : VIRUS
How is the norovirus transmitted and what are its effects?
- transmitted through oral-faecal route OR by direct contact with infected person (through close physical contact, before infected person develops symptoms or after they develop symptoms)
- It causes viral gastrointestinal diseases (common disease : stomach flu)
13.2 FOOD SPOILAGE AND FOODBORNE DISEASES
Which of the following statements is True? (MRQ)
- Consuming a food that has passed its “used by” date will ensure that one does not get food poisoning
- Microorganisms can start to grow in foods after their “Used by” date because the preservatives in food would have been inactivated over time.
- Foods that have a “best before” date will not undergo spoilage
- None of the above
- None of the above
Option 1 : “Use by” date is a safety warning, microbial spoilage will occur after the date and thus may ingest pathogens
(note : spoilage organisms dont make you severely ill, generally do not make you sick but some may be ill due to disgusting odour etc)
Option 2: Preservatives in food only slow down the growth of micrroganisms and DO NOT PREVENT THEM. Hence, even with preservatives, microorganisms can still grow before the “use by” date
Option 3 : undergo spoilage after the best before date, although not always immediately after the best before date in all cases
13.2 FOOD SPOILAGE AND FOODBORNE DISEASES
What is food spoilage caused by?
Caused by high number of spoilage organisms, where they break down macromolecules.
13.2 FOOD SPOILAGE AND FOODBORNE DISEASES
State the kinds of macromolecules that can be broken down by spoilage organisms and their effect. [3]
- Hydrolysis of protein :
- into peptides (short chains of a acids) –> causing food to taste bitter
- into foul-smelling amines, ammonia or sulfur-containing volatiles (hydrogen sulfide, H2S) - Hydrolysis of triglyceride by microbial lipase –> into free fatty acids –> cauing hydrolytic rancidity (off-flavours and odours. Rancidity : bitter, metallic, or soapy aromas
- Hydrolysis of carbohydrates in the cell wall of fruits and vegetables : cause them to become mushy
13.2 FOOD SPOILAGE AND FOOD BORNE DISEASES
What are the three kinds of expiration dates ?
What kinds of food products are they used for and what do they indicate?
- “Use by” – used for highly perishable products ;; it indicates that food is no longer safe to consume after that date
- “Sell by” – used for fresh produce / prepared foods (freshly cut fruits, chilled sandwiches)
- sell by date indicates when retailers need to take item off the shelves
- as rate of detioriation is difficult to predict, manufacturers leave it up to consumer discretion on when to eat it, but usually 1-2 days after purchase
- “Best before” – for products with a very long shelf life
- indicate when food becomes unacceptable to consumers (may be in terms of sensory characteristics)
- food does not change from perfectly fine condition 1 day before the “best before” date to completely spoilt 1 day after the “best before” date
- even after best before date, food is still safe to eat if there are no signs of spoilage –> they are safe indefinitely. canned goods can last for several years as long as no rusting of cans, dents etc
13.2 FOOD SPOILAGE AND FOOD BORNE DISEASES
What are food diseases caused by?
Which category of foods cause the highest percentage of all foodborne outbreaks in the U.S, and how many percent?
- Food diseases are caused by pathogenic microorganisms
- Fruits and vegetables, they accounted for 46% of all foodborne outbreaks in the U.S.
13.2 FOOD SPOILAGE AND FOOD BORNE DISEASES
What are the 2 causes of food poisoning? Define.
- Food intoxication : caused by toxins produced by microorganisms. Even if the micrrogansims are dead, the toxins are heat-resistant and can still be present after food processing
- Food infection : Caused by ingesting pathogens, where bacteria attacks the human body directly and cause diseases.
13.2 FOOD SPOILAGE AND FOOD BORNE DISEASES
- FOOD INTOXICATION
What is the name of the bacteria tha is an aerobic gram positive cocci commony found on human skin?
How does it cause food intoxication and what is the main reason for intoxication?
Staphylococcus aureus
The main reason for intoxication is due to unhygenic handling of food, and heat stable toxins remain in food even after cookng (although microbes are killed during cooking)
13.2 FOOD SPOILAGE AND FOOD BORNE DISEASES
- FOOD INTOXICATION
Micrroganism X is a gram postive anaerobic bacilli (rod-shaped). It grows best in neutral pH and is also known to produce toxins Which of the following microorganisms best matches this description?
- Aspergillius Flavus
- Escherichia coli
- Clostridium perfringens
- Staphylocccocus aureus
- Clostridium perfringens (perfringens makes spores, which are inactive forms of the bacterium that help it survive heat, dryness, and other environmental conditions.)
- More specifically Clostridium Botullinium
13.2 FOOD SPOILAGE AND FOOD BORNE DISEASES
- FOOD INTOXICATION
What are the effects of mycotoxins?
A mycotoxin, aflatoxin is produced by the mould called ____? Where is this mould commonly found?
Mycotoxins weaken immunity and cause cancer over the long term (unlike many toxins that cause gatrointestinal symptoms)
- Aspergillus Flavus , commonly found in grains and legumes WHEN STORED UNDER HUMID CONDITIONS
13.2 FOOD SPOILAGE AND FOOD BORNE DISEASES
- FOOD INTOXICATION
How do toxicoinfections occur?
Pathogens grow to very high numbers in food –> gets ingested –> produces toxins in human body
13.2 FOOD SPOILAGE AND FOOD BORNE DISEASES
- FOOD INTOXIXATION
Name 2 bacteria that cause toxicoinfections
- Bacillus Cerus
- Clostridium Perfringens
13.2 FOOD SPOILAGE AND FOOD BORNE DISEASES
- FOOD INTOXICATION AND INFECTIONS
Why do intoxications cause symptoms more rapidly as compared to infections?
For infections, time is needed for microorganisms to multiply to high enough levels. However, for intoxication, the toxin may already have been formed before ingestion and does not require multiplication of microorganisms
13.2 FOOD SPOILAGE AND FOOD BORNE DISEASES
What are the symptoms of E coli 0157:H7?
Hemorhagic colitis, characterised by bloody stool and kidney failure
13.2 FOOD SPOILAGE AND FOOD BORNE DISEASES
What are some symptoms of clostridium botullinium? [6]
- Constipation
- muscle weakness
- blurry / double vision
- slurred speech
- paralysis
-respiratory failure
13.3 CONTROLLING MICRROGANISMS THROUGH FOOD PROCESSING AND FOOD PRESERVATION
What are intrinsic and extrinsic factors? List the examples.
- Intrinsic factors are conditions within food that affect microorganism growth, such as pH and water activity of food.
- Extrinsic factors are external factors that affect microorganism growth, such as storage temperature and the level of sanitation of working areas
13.3 CONTROLLING MICRROGANISMS THROUGH FOOD PROCESSING AND FOOD PRESERVATION
What are intrinsic and extrinsic factors? List the examples.
- Intrinsic factors are conditions within food that affect microorganism growth, such as pH and water activity of food.
- Extrinsic factors are external factors that affect microorganism growth, such as storage temperature and the level of sanitation of working areas
13.3 CONTROLLING MICRROGANISMS THROUGH FOOD PROCESSING AND FOOD PRESERVATION
How can working areas, such as food processing factories, be sanitised effectively? [2]
- Achieved by proper plant design, training personnel and designing equipment that can be sanitised effectively.
- Establishing efficient cleaning and sanitisation procedure
13.3 CONTROLLING MICRROGANISMS THROUGH FOOD PROCESSING AND FOOD PRESERVATION
What are the benefits of proper santitaion? [3]
- Possible to reduce initial microbial load, therfore minimising microbial spoilage and health hazard
- Produces food that have a long shelf life WHEN properly handled and stored
- Reduce incidence of food-borne diseases
13.3 CONTROLLING MICRROGANISMS THROUGH FOOD PROCESSING AND FOOD PRESERVATION
What is most commonly used technique to kill microorganisms?
heat (thermal processing)
13.3 CONTROLLING MICRROGANISMS THROUGH FOOD PROCESSING AND FOOD PRESERVATION
At a lower heating temperature, cells and spores are _____ injured and stressed. At high temperatures, there is _____ and _____ destabilisation of cells and spores, causing the microorganisms to be killed.
sub lethally ; functional ; structural
13.3 CONTROLLING MICRROGANISMS THROUGH FOOD PROCESSING AND FOOD PRESERVATION
Why are most foods not commercially sterile, when more intense heat treatment for a shorter period of time is more effective than less intense heat treatment for a longer time?
Harsh thermal processing of foods at high heating temperatures cause the largest change in sensory properties of food, which may not be desirable.
13.3 CONTROLLING MICRROGANISMS THROUGH FOOD PROCESSING AND FOOD PRESERVATION
What is the limitation of less drastic thermal processing?
For less drastic heat treatment, how do we ensure that all microoganisms are killed?
- In less drastic thermal processing, not all microorganisms are killed and other preservation technologies need to be employed
- Can couple less drastic heat treatment with other food preservation methods, such as low-temperature storage, storing at low moisture etc…
13.3 CONTROLLING MICRROGANISMS THROUGH FOOD PROCESSING AND FOOD PRESERVATION
What is the optimal temperature for bacterial growth?
What is the general rule of thumb for the “danger zone” (temperature and time) for prepared foods?
- 10-35°C (bacteria double every 30 min)
- Prepared foods should not be stored at 5-60°C for more than 4 hours
13.3 CONTROLLING MICRROGANISMS THROUGH FOOD PROCESSING AND FOOD PRESERVATION
How does vacuum packing prevent the growth of microorganisms?
- It deprives aerobic bacteria, yeast and moulds of O2
13.3 CONTROLLING MICRROGANISMS THROUGH FOOD PROCESSING AND FOOD PRESERVATION
Most yeasts and moulds are strictly aerobic. True or False?
True, except for a few anaerobic yeasts and moulds thaat are involved in anaerobic fermentations.
13.3 CONTROLLING MICRROGANISMS THROUGH FOOD PROCESSING AND FOOD PRESERVATION
How can we control the water activity of foods? [2]
- Dehydrating food
- Adding salt/sugar
13.3 CONTROLLING MICRROGANISMS THROUGH FOOD PROCESSING AND FOOD PRESERVATION
_____ tend to grow best and outcompete other microbes at high water acitivity. This microorgansim also grows best in _____ pH.
As water activity drops, _____ and _____ are most likely to outcompete and predominate the microbe stated above. They grow best in relatively _____ pH.
bacteria ;; neutral ;; yeast, mould ;; lower
13.3 CONTROLLING MICRROGANISMS THROUGH FOOD PROCESSING AND FOOD PRESERVATION
Preservatives, such as organic acids, sulfites and nitrites are also considered intrinsic factors of food. True or False?
True
13.3 CONTROLLING MICRROGANISMS THROUGH FOOD PROCESSING AND FOOD PRESERVATION
Preservatives, such as organic acids, sulfites and nitrites are also considered intrinsic factors of food. True or False?
True
13.3 CONTROLLING MICRROGANISMS THROUGH FOOD PROCESSING AND FOOD PRESERVATION
What is hurdle technology?
It is a method of controlling the growth of microorganisms by combining intrinsic and extrinsic factors.
13.3 CONTROLLING MICRROGANISMS THROUGH FOOD PROCESSING AND FOOD PRESERVATION
What are the 2 benefits and the disadvantage of hurdle technology?
Benefits :
1. When multiple intrinsic and extrinsic factors are combined, they can extend shelf life using milder treatment
- Combination of intrinsic and extrinsic factors can prevent the growth of microorganisms, but controlling each instrinsic / extrinsic factor by itself is not fully able to stop microorganism growth
Disadvantage :
- Due to large number of possibilities in combination of intrinsic andd extrinsic factors, extensive scientific research is needed to validate anti-microbial efficiency of hurdle technology in food systems.
13.4 FERMENTED FOODS AND FOOD FERMENTATION
What is the definition of fermentation?
It refers to metabolic processes that take place during desirable microbial growth, resulting in evident physical and chemical changes to food materials. (e.g colour, texture, flavour, nutrients)
13.4 FERMENTED FOODS AND FOOD FERMENTATION
What is the idea behind fermentation?
the idea is to let microorganisms fermenting the food outgrow other harmful microoganims, preventing spoilage
13.4 FERMENTED FOODS AND FOOD FERMENTATION
What is meant by biotransformation of food components?
Using natural processes to transform raw materials into ingredients that improve flavour, digestibility, and/or shelf life of food.
13.4 FERMENTED FOODS AND FOOD FERMENTATION
What are the three types of fermented foods?
- acid-fermented foods
- alkaline-fermented foods
- alcohol-fermented foods
13.4 FERMENTED FOODS AND FOOD FERMENTATION
What is the most common class of bacteria used for acid fermentation?
Lactic acid bacteria
13.4 FERMENTED FOODS AND FOOD FERMENTATION
What are the 2 kinds of bacteria that ferments yoghurt? Why are 2 kinds o bacteria needed?
- Lactobacilus Delbrueckii : can grow quickly but can only bring pH down to 5.5 (cuz its growth is inhibited by low pH)
- Streptococcus Thermophilus : can bring pH of yoghurt down to a final pH of 4.5, but grows slowly
2 kinds of bacteria needed to increase rate of growth of bacteria, and to lower pH to low enough levels
13.4 FERMENTED FOODS AND FOOD FERMENTATION
Lactobacillus plantarum, Leuconostoc spp and Pediococcus spp are bacteria used to _____ bring down the pH of _____
progressively ;; kimchi
13.4 FERMENTED FOODS AND FOOD FERMENTATION
What is the idea behind alkaline fermentation?
Hydrolysis of protein to amino acids, and amino acids further hydrolysed to produce ammonia.
13.4 FERMENTED FOODS AND FOOD FERMENTATION
What type of microorganism is used to ferment:
1. Natto
2. Tempeh
give the name too.
- Bacillus Subtilis (gram-positive bacteria)
- Rhizopus Oligosporus (mould)
13.4 FERMENTED FOODS AND FOOD FERMENTATION
What is the idea behind alcoholic fermentation?
Sugars in food are being converted to alohol, usuall by yeast.
13.4 FERMENTED FOODS AND FOOD FERMENTATION
What is the idea behind alcoholic fermentation?
Sugars in food are being converted to alohol, usuall by yeast.
13.4 FERMENTED FOODS AND FOOD FERMENTATION
Which yeast is used to ferment wine and beer, and to act as a leavening agent in the fermentation of bread dough?
Saccharomyces Cereviside
13.4 FERMENTED FOODS AND FOOD FERMENTATION
Why do we not taste alcohol in sourdough breads, though it is produced in the fermentation of dough?
- It is produced in small amounts
- It would have largely evaporated off in the baking process
13.4 FERMENTED FOODS AND FOOD FERMENTATION
List the 4 benefits of food fermentation
- Alters sensory properties of food, generating new odours and taste to compounds [e.g. in alkaline fermentation, glutamic acid, an a acid can be produced ;; amino acids can react in millard reaction with reducing sugars to form pigments]
- Fermentation break down cell walls and antinutritive factors, increasing bioavailability of nutrients.
- Microorgansms fermenting foods can produce some vitamins and thus increasing its nutritional value.
- Fermentation can preserve foods, as it produces anti-microbial compounds such as organic acids and alcohol.
13.4 FERMENTED FOODS AND FOOD FERMENTATION
What is a disadvantage of fermentation?
- Microoganisms that ferment foods can become food spoilage organisms when their growth is unwanted/ undesirable in another food product.
e.g. if yeast were allowed to ferment and grow in yoghurts, it produces gas and causing bulging of yoghurt (texture). It can also produce alcoholic off flavours. (flavour)
